1. Field of the Invention
This invention relates to electrorheological fluid compositions. More particularly, it relates to electrorheological fluid compositions which excel in electrorheological properties in the presence of an electric field as manifested in the phenomenon of generating a large shear stress in response to even a relatively weak electric field applied thereto and consequently causing the current density existent therein to remain at a depressed level during the presence of the large shear stress, also excel in the ability to stabilize the high shear stress and the low current density enough to defy the effect of aging, and find utility in devices of all types operatable with electrorheological fluids such as, for example, actuators for transmission of torque represented by clutches and brakes and actuators for regulation represented by engine mounts, dampers, and valves, and in ink of electrorheological fluid for ink jet system.
2. Description of the Prior Art
The electrotheological fluid is a fluid which is obtained by dispersing and suspending disperse-phase particles of a varying solid substance, for example, in an electrically non-conducting oil and which has rheological properties or properties of flow thereof transformed by increasing electric field strength into visco-plastic properties. Generally, it has been known as a fluid which manifests the so-called Winslow effect, namely the effect of notably gaining in viscosity and inducing a large shear stress in response to an external electric field applied thereto. Since the Winslow effect is characterized in that the viscosity of the electrorheological fluid can be freely controlled with an electric signal and the control can be attained at an extremely high response speed, attempts are being made to adapt electrorheological fluids for use in actuators such as clutches, brakes, engine mounts, dampers, and valves and in ink of electrorheological fluid for ink jet system.
Heretofore, as electrorheological fluids, those products which are obtained by dispersing solid particles such as of cellulose, starch, soybean casein, silica gel, a polystyrenic ion-exchange resin, and a cross-linked polyacrylate in electrically nonconducting oils such as silicone oil, chlorinated biphenyl, and transformer oil have been known to the art.
The electrorheological fluids which use cellulose, starch, and soybean casein as a disperse-phase, however, have a problem of deficiency in the shear stress to be generated in response to an electric field applied thereto. The electrorheological fluids which use a cross-linked polyacrylate as a disperse-phase have a problem of inability to induce a practically sufficient shear stress in response to application of a relatively weak electric field thereto.
The electrorheological fluids which use an ion-exchange resin of the form of an alkali metal salt of polystyrenesulfonic acid, one of the polystyrenic ion-exchange resins, as a disperse-phase derive a large shear stress from application of even a relatively weak electric field. They nevertheless have a problem of large growth of the current density existent therein and deficiency in the ability to stabilize the generated shear stress and current density enough to resist the effect of aging.
The present invention is directed to solving the problems encountered by the conventional electrorheological fluids as described above.
An object of this invention, therefore, is to provide an electrotheological fluid composition which excels in electrorheological properties in the presence of an electric field as manifested in the phenomenon of generating a large shear stress in response to even a relatively weak electric field applied thereto and consequently causing the current density existent therein to remain at a depressed level during the presence of the large shear stress and further excels in the ability to stabilize the generated large shear stress and low current density enough to defy the effect of aging.